Method of roughening the surface of ferrous elements



Dec. 30, 1947. c. A. EscoFl-'ERY x-:T AL 42,433,353

Filed March 13, 1946 ,j/ INVENToRs.

QZgfs/isw er y BY 5111762 il@ ,/ef/j Patented Dec. 30, 1947 METHOD l oF ROUGHENING 'rent SURFACE 0F lFimRoUs ELEMENTS Charles A. Escoffery, East Orange, and Burton Werbel, Newark, N. J., `assignors .to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application March 13,1946, Serial No. 654,204

This invention relates to novel articles of manu-l facture and to methods for preparing the same.

In its more specific aspect, the invention is directed to novel rectiers, parts thereof and to methods for preparing the same. The rectiflers with which this invention is more particularly concerned are thosegenerally known as the dry or dry disc type.- y

These dry rectiers generally consist of a fer rous base plate carrying thereon' a layer of selenium on top owhich is an eutectic alloy, such as Woods alloy. In some instances between the 45 Claims. y(Cl. 421-42) ferrous base and the selenium layer there may be va thin layer of nickel, iron or the like.

Figure l is a top plan view of adry rectifier embodyizig the present invention.

Figure 2 is a cross sectional view taken on line 2-2 of Figure 1. said view being greatly magnifled.

The general process employed in producing a selenium rectifier consists in applying a layer of selenium to a metallic base plate, such as iron VIn the course of our experimentations, we have discovered vthat we may produce dry disc rectifiers which are' superior to the prior art rectiiers of this type. We have further found that we may treat the base metal to provide a surface which has improved adherence where selenium is deposited thereon. This treatment 4is silent, fast, easily controlled and relatively inexpensive. In addition it presents no hazard to health and does not introduce an additional electrical resistance in the rectifier.

We have further discovered that an improved etched surface'may be produced by simply immersing the base metal in a vnovel bath fora limited period of time. After [this immersion step, the basemetal has a smut thereon. Most or practically all of this smut may be readily and easily removed` by simply treating the smut cov- 'ered surface with water.

Briefly, in carrying out this invention we pre- -lfer to employ a ferrous base plate I and preferand usually steel and thenl spraying on to the layer of selenium a layer of a, fusible eutectic alloy, such as Woods alloy. The metallic base plate and the alloy constitute the two electrodes of the rectifier.

In practice, no serious diilculties are ordinarily by blasting with an abrasive such as sand, during v which treatment surface oxides may also be removed.

It has long been known that while this sandblasting treatment provided a surface ,on the base plate which provided a better adherence surface for selenium thereto than the untreated .base plate, this adherence characteristic was only moderately good and therefore was far from being completely satisfactory. Other disadvantages of Sandblasting are: sometimes sand particles are e embedded in the so treated base, high cost, time consuming, noisy, inconvenient and presents a silicosis hazard. Consequently, various attempts have been made to treat the base metal inY various manners in order to provide a better adhering surface between the base and the selenium, All of these have failed for one reason or another and generally because such treatments introduce an electrical resistance in the completed recti- "iier which is reected as a low'forward grade or a low forward conductivity characteristic.

ably one whose carbon content is no greater than about .5%. While pure irongmay be employed, foreconomic reasons We prefer to employ steel having a hardnessno greater than on th Rockwell B scale and a carbon content no greater Y subjected to a cleaning operation 'to remove the oil, grease and dirt thereon. While any number of different methods maybe employed for this v purpose, we prefer to accomplish that purpose by employing either an alkali soakvcleaning or an alkali electrocleaning step and more preferably the latter. For this cleaning step we prefer to employ an alkali cleanser, such as Oakite manufactured by the Oakite Products, Inc., of New York, New York. A water solution of said Oakite #90 is made up with the concentration' of said solution being about 8 ounces Oakite #90 per gallon of water. The solution is heated to about its boiling point or about 5 to 10 degrees F. therebelow and said blanks l are placed therein andare connected to the positive pole of a source of E. M. F. and the negative pole is connected to the container of said solution and thisA container may also be steel. It is preferable to employ separate steel elements immersed in said solution as the cathodes. The current density of the anode or blank I Abeing treated in said solution at said temperature is about 50 amperes per square foot. At the end of three minutes, the blanks I will be found to be clean and are removed from said solution. Then the blanks are rinsed in a hot water bath- By whatever method employed, the cleaned ferrous base blanks I are now ready for treatment to roughen or deep etch the exterior surface thereof.

According to this invention, these cleansed ferrous'base blanks I are immersed in a novel etching solution in order to etch or roughen the same. This solution consists of an aqueous solution of nitric acid and acetic acid and for best and most eiicient operation and results, the solutions consist of 50 to 55 parts by volume of acetic acid, 40

parts by volume of concentrated nitric acid (42v Baume) and 40 to 55 parts by volume of Water. During treatment of said blanks I in any of said solutions, the temperature of said solution is maintained in any convenient manner in the range of about C. to 45 C. and more preferably in the range of about 19 C. to 32 C. The bath or solution may be constantly stirred or agitated by means of a mechanical stirrer or by air agitation to improve the appearance of the discs or blanks, to prevent stratification and to aid in leveling the temperature of the solution throughout its mass. After a period of about .5 to about 6 minutes in said solution, the blanks I are removed and immediately thereafter are treated with water, by spraying or rinsing to remove the smut therefrom. The rinse or spray water may be at room temperature, but We prefer it be higher and about 150 F.

Upon removal of the smut, the surface of each blank I presents an exposed surface characterized by a number of pits, elevations and irregu..

larities for locking the selenium thereto and thus provide good adherence characteristics. Thedeep etching produced by this invention exhibits a marked degree of'undercutting (shown in Figure 2) which is probably the cause of the excellent adherence thereto of a selenium layer 2 added thereto: and in addition shows a much greater surface area when compared with a sandblasted surface. If desired, an intermediate layer of nickel, iron, cobalt 3 or the like may be deposited on the etched surface of said ferrous base I after which the layer 2 of selenium may be deposited thereon. Ordinarily, a layer of nickel is electro-deposited thereon and when this is to be done, we prefer to immerse the blank I,

l after the smut has been removed therefrom, into an aqueous solution of hydrochloric acid fora short time in order to activate the etched surface thereof before electroplating. The hydrochloric 'acid solution may have a concentration of about 10-20% and the time of immersion therein is between about one to three minutes. Either with or without the intermediate layer, the selenium layer will have good adherence to said roughened surface and good electrical characteristics, On to said selenium layer 2 may be deposited a layer 4 of a fusible eutectic alloy, such as Woods alloy.

The following are illustrative examples' of specific solutions which we have found to be particularly efficacious in the practice of this invention:

Solution I Parts by volume Glacial acetic acid 50 Concentrated nitric acid (42 Baum) 40 Water 40 Solution II Parts by volume Glacial acetic acid 55 Concentrated nitric acid (42 Baum) 40 Water 45 Solution III v Parts by volume @Glacial acetic acid 55 *Concentrated nitric acid (42 Baum) 40 Water 50 Solution IV j Parts by volume Glacial acetic acid 50 Concentrated nitric acid (42 Baum) 40 Water -c 55 In the practice of this invention, into a glass or other appropriate container may be poured to55 parts by volume of water and then there is added thereto 40 parts by volume of concentrated nitric acid (42 Baum) and'50 to 55 parts by volume of glacial acetic acid. Then into said solution is immersed a metallic base blank I and preferably a carbon steel blank having a carbon content no greater than about 0.5% and preferably between about 0.05 and 0.5% and a hardness no greater than 85 and preferably no lower than 30 on Rockwell B scale. The steel blank I is allowed to remain in one of said solutions for a period of about l to 6 minutes during which time said solution is agitated and maintained between about'15" C. and 45 C. Then the sotreated blank is removed therefrom and is subjected to a water rinsing or spraying operation whereby the smut is removed therefrom. After the smut has been removed from said blank,

the blank may be immersed for a period of about 1 to 3 minutes in an aqueous solution of hydrochloric acid. This aqueous solution of hydrochloric acid may be prepared by adding 20 parts by volume of concentrated hydrochloric acid to parts by volume of water. Then the disc is ready for nickel plating, after which a layer of selenium is deposited thereon and onto said layer of selenium may be deposited a layer of a fusible eutectic alloy, such as Woods metal. The nickel may be completely substituted by electrolytic iron, cobalt or the like and in some instances, no intermediate layer need be present between the base material and the selenium. The dry rectiiiers whose ferrous electrodes and particularly, those of the type heretofore delned, have been etched in accordance with this invention and with or without an intermediate layer between the selenium and the so-etched surface have improved electrical and mechanical properies.

While this invention has been described in considerable detail, it is not to be limited thereby because various changes and modifications may be made within the scope of this invention without departing substantially from the spirit thereof.

We claim:

1. The method of etching a ferrous element comprising treating said element with a solution comprising 50 to 55 parts by volume of acetic acid, 40 parts by volume of concentrated nitric acid and 40 to 55 parts by volume of water.

2. The method comprising treating a ferrous I' element with a solution maintained in the range of 15 C. to 45 C. and comprising 50 to 55 parts u by Volume of acetic acid, 40 parts by volume of concentrated nitric acid and 40 to 55 parts by volume of water.

5 3. The method of etching a ferrous element comprising treating said element with a solution comprising 50 to 55 parts by volume of acetic acid, 40 parts by volume of concentrated nitric acid and 40 to 55 parts by volume of water, said element being treated with said solution until smut is produced on one sui-face thereof and Water to remove said smut from said surface.

5. A method comprising roughening a surface of a low carbon steel having a carbon content no greater than 0.5% with a solution of 50 to 55 parts by volume of acetic acid, 40 parts by volume of concentrated nitric acid and 40 to 55 parts by volume of Water.

' CHARLES A. ESCOFFERY.

BURTON WERBEL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,376,369 Wertheimer Apr. 26, 1921 2,177,751 Sikorski Oct. 31, 1939 2,411,532 'Escoiery Nov. 26, 1946 

